The present invention relates generally to a reciprocating pump. More particularly, this invention concerns an improved downhole pump for producing a well.
In elevating a subsurface fluid, a pump is positioned within a wellbore and adjacent to a geological formation containing the fluid. The downhole pumps of the prior art have traditionally comprised a plunger reciprocating within a pump barrel located at or near the end of tubing extending downward through the casing of the well. The downhole pumps of the prior art are generally characterized by the use of two independent valves to accomplish the pumping action. A standing check valve is secured in the pump barrel beneath the plunger, which includes a traveling check valve. The upstroke of the plunger opens the standing valve and draws fluid into the pump barrel as the traveling valve remains closed. The downstroke of the plunger opens the traveling valve and forces upward the fluid from the pump barrel as the standing valve remains closed. The fluid is thus raised through the tubing by repeated pump cycles.
The downhole pumps of the prior art function satisfactorily with liquids only, but are prone to a condition known as gas lock when pumping a combination of liquid and gas. In a gas lock condition, gas trapped in the pump barrel simply expands or compresses with reciprocation of the plunger so as to prevent operation of either the standing valve or the traveling valve. The pressure within the pump barrel locks the standing and traveling valves closed. Oscillation of the plunger is thus ineffectual to accomplish pumping because both valves stay closed. Production of the well must then be interrupted to relieve the gas lock condition, which is time consuming and therefore expensive. Since crude oil is usually accompanied by natural gas, it will be appreciated that gas lock is a problem of considerable magnitude in the petroleum industry. There is thus a need for a new and improved downhole pump of no susceptibility to gas lock.
The present invention comprises an improved downhole pump which overcomes the foregoing and other problems which have plagued the prior art. In accordance with the general aspects of the invention, there is provided a downhole pump which accomplishes pumping by positive displacement below the standing valve and in the absence of a traveling valve. The volume defined by a plunger and a slidable pump barrel is vented on the downstroke of each pump cycle. The downhole pump of the invention is therefore immune to gas locking and is capable of operation in the presence of a mixture of incompressible and compressible fluids. Use of the downhole pump of the present invention results in greater pumping efficiency and eliminates the expenses which would otherwise be incurred by interrupting production of a well to relieve a gas lock condition.
In accordance with more specific aspects of the invention, an improved downhole pump includes a pump body for attachment to the end of tubing arranged in the casing of the well. A pump barrel extending from the bottom end of the pump body is slidably mounted for axial movement responsive to stroking of a plunger or piston. The pump barrel can be either magnetically or mechanically responsive to movement of the piston. Ports are provided in the pump barrel for fluid communication. The plunger or piston inside the pump barrel is reciprocated by a plunger rod extending through the center of the pump body. On the upstroke, the pump barrel moves upward to the limit of its travel until certain of the ports in the barrel register with passageways leading to the top of the pump body and having check valves located therein. The fluid in the pump barrel is thus positively displaced upwardly by the piston. On the downstroke, the pump barrel moves downwardly to the lower limit of travel closing the passageways in the pump body and opening the ports in the pump barrel to vent any incompressible fluid trapped therein. Due to the self-relieving design and the fact that the lifting action takes place below the standing valve, pumping of liquids and gases in combination can be accomplished without gas lock by means of the improved downhole pump of the present invention.